1. Field of the Invention
The present invention relates to a control system for a plant, and particularly to a control system that controls a plant with the sliding mode control so that a controlled output of the plant coincide with a target value.
2. Description of the Related Art
Japanese Patent Laid-open No. 2003-15703 (JP '703) discloses a control system which performs a feedback control with the sliding mode control. According to this control system, a feedback control is performed with the sliding mode control so that an opening of a throttle valve of an internal combustion engine coincides with a target opening, for example.
In the above conventional control system, a model parameter identifier is used in order to deal with a change in the dynamic characteristic of the controlled object, and model parameters of a controlled object model which is obtained by modeling the controlled object are identified in real-time processing.
However, if the change in the dynamic characteristic is comparatively large, disturbance applied to the controlled object is comparatively large, or the controlled object has nonlinear characteristics, a modeling error (a difference between the characteristic of an actual controlled object and the characteristic of the controlled object model) temporarily becomes large, and control stability may be reduced.
Further, in the above conventional system, a method in which influence of the disturbance is eliminated by one model parameter (c1) identified by the model parameter identifier, is adopted. Accordingly, there is a possibility that the control system can not sufficiently deal with the change in the dynamic characteristic of the controlled object.